Structures for suspending sheets to define environmentally controlled spaces are well known. The U.S. Pat. Nos. 4,860,778 to Pohl and 5,224,306 to Cramer exemplify such structures. These prior art systems employ a U-shaped strut with a sheet retained against the interior of the strut by a cap frictionally held between the legs of the U-shaped strut. Similar retaining devices are disclosed in U.S. Pat. Nos. 4,410,027 to Lucous and 4,694,543 to Conley.
However, all of the prior art devices present a significant projection form the plane of the retained sheet.